As well known, liquid crystal display (LCD) devices have a high contrast ratio and low energy consumption, and are suitable to display gray scale images and moving images. Thus, LCD devices are most widely used as a representative example of flat panel display devices, and are being actively developed.
In particular, because of a lot of outstanding advantages such as thinness, light weight, and considerably reduced energy consumption as compared to cathode ray tubes (CRTs), various applications of LCD devices are possible in association with not only ultra-thin display devices of wall mounted TV sets, but also monitors of notebook computers that use a battery as a power source. Accordingly, LCD devices are highlighted as next-generation display devices.
Such an LCD device generally includes a thin film transistor array substrate in which thin film transistors and pixel electrodes are formed at respective pixel defined by gate lines and data lines, a color filter layer array substrate having a color filter layer and common electrode, and a liquid crystal layer interposed between the two substrates. In the liquid crystal display device having the above described configuration, liquid crystal molecules of the liquid crystal layer are rearranged when a voltage is applied to electrodes. The quantity of light passing through the liquid crystal layer is regulated based on the degree of rearrangement of the liquid crystal molecules, to display an image.
In this case, both the color filter layer array substrate and the thin film transistor array substrate are bonded to each other by a sealant such as epoxy resin. The thin film transistor array substrate is connected to drive circuits on a printed circuit board (PCB).
Specifically, as shown in FIG. 1, the thin film transistor array substrate 10 is divided into an active region 10a at the inside of a dotted line, the active region being an image display region, and a pad unit region 10b at the outside of the dotted line. The active region 10a includes a plurality of gate lines 61 and data lines 62 orthogonally intersecting each other to define unit pixels, and thin film transistors (TFTs) formed at intersections of the gate lines 61 and data lines 62. The unit pixels include pixel electrodes 70, respectively. The pixel electrodes 70 are connected to the respective TFTs, to display an image by switching of the respective TFTs.
The pad unit region 10b includes gate pads 61a and data pads 62a which are extended from the gate lines 61 and data lines 62, respectively. The gate pads 61a and data pads 62a are connected to external drive circuits, respectively, by interposing gate drive ICs and data drive ICs, to receive various control signals and data signals. The external drive circuits are integrated on a board, more particularly, a printed circuit board, and are adapted to produce the various control signals and data signals required to drive the LCD device.
Specifically, the gate pads 61a serve to apply scan signals in sequence to the plurality of gate lines arranged in the active region, and the data pads 62a serve to apply data signals in sequence to the plurality of data lines arranged in the active region.
When the gate lines receive the scan signals via the gate pads, and thus the TFTs that are connected to the gate lines are turned on, the data signals applied from the data pads are transmitted to the respective pixel electrodes, so as to display an image.
Prior to being bonded to the color filter layer array substrate, the above described thin film transistor array substrate must be subjected to a mass production system (MPS) test for testing various defects such as line defects and point defects. In the MPS test, a signal voltage is applied to the thin film transistor array substrate via the gate pads and data pads that are connected to the gate lines and data lines in the active region, respectively, to determine whether or not the thin film transistor array substrate has defects.
For example, to perform a vision auto probe (VAP) test for testing defects of the respective unit pixels, probes, to which predetermined signals are applied, are accurately aligned with the gate pads and data pads, such that the gate pads receive the associated predetermined signals and the data pads receive the associated predetermined signals. In accordance with the reception results, it can be confirmed whether or not a desired image is displayed on the respective unit pixels. In this case, a VAP test apparatus is divided into a panel having the probes for applying the predetermined signals to the gate pads and a panel having the probes for applying the predetermined signals to the data pads. The probes are fabricated to be accurately aligned with the gate pads and data pads, respectively.
However, the conventional liquid crystal display device has the following problems.
The plurality of gate pads and data pads, which are extended from the gate lines and data lines, are divided into several groups. With this arrangement, however, widths between the gate pads and between the data pads are narrow, and each of the gate pads and data pads has a small size, making it difficult for the probes to come into accurate contact with the gate pads and data pads. When the probes fail to contact at accurate positions, it is impossible to apply the predetermined signals to the gate pads and data pads, and therefore, defects of pixels cannot be confirmed.